A conventional stationary bike 6 is shown in FIG. 7 and generally includes a frame 62 with a driving device 61 connected thereto and the driving device 61 includes a driving wheel 611 mounted on a first shaft 621 and a flywheel 63 is connected with a second shaft 623. A belt 612 is connected between the driving wheel 611 and the flywheel 63. Two cranks 622 are connected to two ends of the first shaft 621 and are rotated by the user to drive the driving wheel 611. Some stationary bikes include a magnetic resistance device 64 and/or an electric power generation device 65. The magnetic resistance device 64 generates a resistance force to the flywheel 63 to provide the exercise purpose. The power generation device 65 includes a stator 652 and permanent magnets 651 which move relative to the stator 652 to generate electric power which powers the control panel 66 and the magnetic resistance device 64.
The driving device 61, the flywheel 63, the magnetic resistance device 64 and the power generation device 65 have to be installed to the frame of the stationary bike 6 according the profile and shape of the frame, this requires a lot of time and skilled persons. Besides, the first and second shafts 621, 623 require a large space so that the stationary bikes are bulky and occupy large transportation space.
The present invention intends to provide a compact driving and resistance device for stationary bikes, the flywheel and the magnetic resistance wheel share a common shaft so that the stationary bikes can be compact and the assembly time can be reduced.